Switching regulator with rapid switching drive

ABSTRACT

A switching type regulator reduces switching transition times by increasing the magnitude of the switching control signal at the exact interval of the occurrence of the switching transition. The magnitude of the switching control signal is in turn responsive to the output voltage and hence the circuitry to reduce switching transition times also functions to regulate the output voltage.

United States Patent Inventor Eric V. Madsen New Shrewsbury, NJ. Appl.No. 823,120 Filed May 8, 1969 Patented May 18,1971 Assignee BellTelephone Laboratories, Incorporated Murray Hill, Berkeley Heights, NJ.

SWITCHING REGULATOR WITH RAPID SWITCHINGDRIVE 6 Claims, 3 Drawing Figs.

u.s.c| 323/22, 323/38 lnt.C| G05f 1/56 FieldoiSearch 321/2,18,

l9;323/4,l6, 17,18, 22 (T), 22 (ER), 38

Primary ExaminerJ. D. Miller Assistant Examiner-A. D. PellinenAttorneys-R. J. Guenther and E. W. Adams, Jr.

ABSTRACT: A switching type regulator reduces switching transition timesby increasing the magnitude of the switching control signal at the exactinterval of the occurrence of the switching transition. The magnitude ofthe switching control signal is in turn responsive to the output voltageand hence the circuitry to reduce switching transition times alsofunctions to regulate the output voltage.

313 LOW PASS 6H2 [wHLTER 34g) SWITCH CONTROL AND L i THRESHOLD DETECTORI T0 H l tcousmzml L :.J 7 |.&A 0 350 as: I; 25 gg gggr SWITCHING DEVICEd DISABLEFD I $323 3|8 I TWO LEVEL CURRENT SOURCE g u /CURRENT DETECTORI 327 -333 E: Di t ISM-'25 5 a j 1; fax 302 4 Patented May 18, 1971 2Sheets-Sheet 1 IIo H3 M LPF E T I TO L 47- III LOAD I20 I 25 CIRCUIT r-I05 x T SWITCH THRESHOLD ggsggg 435 I -J CONTROL DUTCH DISABLER Hi5 I fCURRENT r 7 LEVEOL I DETECTOR CURRENT IoI SOURCE II I T -v FIG. 2 TIMINGDIAGRAM 2I2 INDUCTOR +v I VOLTAGE 0 2| Ia ZE 222 Lh -T OUTPUT 225 220VOLTAGE 0 23 CURRENT 21 233 SOURCE 1 2 L OUTPUT I 232 Q I I INVENTOR E.L MADSEN ATTORNEY BACKGROUND OF THE INVENTION This invention relates topower converters and more particularly to a switching type powerregulator and to switching control circuitry therein to increase theregulator switching speed.

Power converters accept energy from an unregulated energy source such as.a voltage source and derive therefrom a regulated voltage applied to aload circuit. This regulation function is performed by interposing aregulating device between the source of energy and the load circuit. Theregulating device normally comprises a controlled variable impedanceinterposed between the source and the load. This variable impedance iscontinuously varied in its impedance magnitude in order to maintain aconstant voltage or current at the load circuit. These variableimpedance devices, unfortunately, dissipatesignificant amounts of' thepower transmitted from the source to the load.

Switching type regulating devices control the rate of energytransmission in a discontinuous manner and consume less power in theirregulating action than do the above-described variable impedance typeregulating devices. The switching type regulating device is normallyinterposed between the source of energy and the load. The switchingdevice theoretically has only two modes of operation: conduction andnonconduction. The switching device periodically conducts for a timeinterval sufficient to maintain the power output at a certainpredetermined level. The periodic conducting time interval of theswitching device is changed to'correct the power output should itdeviate from its predetermined level.

The magnitude of the power delivered to the load circuit is directlydependent upon the duty cycle of the switching device, that is, theratio of its conducting time to its nonconducting time. It is apparentthat since the switching device either fully conducts with a very lowimpedance or does not conduct at all, the power dissipated therein isvery small. Hence, a switching type regulator is very efficient intransferring power from the source to the load'as compared with theconventional regulator utilizing a variable impedance.

' More switching type regulators utilize semiconductor devices, suchaspower transistors, as the switching device. The semiconductor device isfully saturated when it is conducting, and hence very little power isdissipated therein. The semiconductor device in its nonoonductingcondition is fully turned off and again no power is dissipated therein.Power,

. however,.is dissipated in the semiconductor device during the timeinterval of the switching transition from the nonconducting condition tothe conducting condition and vice versa. Hence during this switchingtime interval a substantial amount of power may be dissipated in thesemiconductor device. This power dissipation, if large enough, maydamage the semiconductor device.

It is an object of the invention to reduce the power dissipation in thesemiconductor device during its switching interval from one conductionstate into another conduction state.

It is another object of the invention to reduce the switching transitiontime interval of a switching type regulator to a minimum.

SUMMARY OF THE INVENTION Therefore in accord with the present invention,a circuit arrangement is included in a switching type regulator toincrease the speed at which the switching device switches from oneconduction state into the other conduction state.

i In one particular embodiment of the switching type regulator,nonregulated voltage source is repeatedly connected to and disconnectedfrom an energy storage element such as an inductor. This energy storageelement or inductor is in turn coupled to an output load circuit. Thesemiconductor switching device is energized, via a switch controlcomprising a driver transistor, which in turn is controlled by a twolevel current source. The two level current source is coupled to theoutput voltage sensing impedance and to the control electrode of thedriver transistor. The necessary current to bias the driver transistorinto a conducting condition becomes available only when current in theoutput control impedance drops below a certain level. As the drivertransistor initially begins to conduct, the current source is switchedinto a higher level current condition in order to supply additionalcurrent to speed up tum-on in the driver transistor. Hence, the speed oftum-on of the semiconductor switching device, controlled by the drivertransistor, is also increased significantly. This increased switchingspeed reduces power dissipation in the semiconductor switching device.

An advantage of the circuit of the invention is that the two levelcurrent source, by responding to a drop in the current in the outputcontrol impedance, regulates the output voltage.

BRIEF DESCRIPTION OF THE DRAWING Many additional features, advantagesand other objects of the invention will become apparent uponconsideration of the following detailed description of a specificswitching type regulator embodiment utilizing the principles of theinvention. The following description is to be taken in conjunction withthe attached drawings in which:

FIG. 1 is a block diagram of a switching type regulator embodying theprinciples of the invention;

FIG. 2 shows waveforms which illustrate the operation of the circuitshown in FIG. I; and

FIG. 3 is a detailed schematic diagram of a regulator circuit in accordwith FIG. 1 embodying the principles of the invention.

DETAILED DESCRIPTION The switching type regulator disclosed in FIG. 1 isconnected to a voltage supplied by a DC voltage source 101 which maycomprise a battery. The regulated voltage supplied at the outputterminal 140 is derived from the voltage source I01. This regulatedvoltage has a polarity opposite the polarity of the voltage supplied bythe source I01. While the switching regulator illustrated by way ofexample herein alters the polarity of the regulated voltage from thesource voltage, it is to be understood that the principles of theinvention are equally applicable to switching type regulators in whichthe regulated output voltage is the same polarity as that of the voltagesource 101.

The voltage supplied by the source 101 is coupled, via a currentdetector I I5 and a switching device shown schematically in FIG. 1 as asimple switch 105, to an energy storage device or inductor 110. Theinductor 110 preferably includes a magnetic core to facilitate thestorage of magnetic flux. The switch 105 is preferably a semiconductorswitching device.

Upon closing the switch 105, a current in response to energy supplied bythe source 101 is transmitted through the inductor 110. As a result ofthis current, energy is stored in the inductor in the form of magneticflux stored in its core. When the switch 105 is opened the energy storedin the inductor 110 is released and transmitted, via the diode 112, anda low pass filter 113 to the output terminal 140. The regulated outputvoltage at the output terminal is derived from the The typicalregulation cycle normally begins at the time 1,, as shown in FIG. 2',when the switch 105 is initially closed in response to the switchcontrol 120. With the switch 105 closed, energy is coupled from thesource 101 to the inductor 110. A current begins to flow from groundthrough the inductor 110 and the switch 105 to the negative voltagesource 101. As shown by the waveform 210 in Fig. 2, the voltage at theterminal A in FIG. 1 drops to the negative voltage of the source 101 attime 2,. This is shown by the voltage level 211. As will be explainedbelow, the two level current source 130, at the time t,, is switchedinto its high level conduction state, as shown by current level 231 inwaveform 230.

The current flowing from ground through the inductor 110 to the negativesource 101 stores energy in the inductor 1 in the form of magnetic flux.Due to the increase in the current through the detector 115, the voltageat point A increases as indicated by the positive slope 211a of thevoltage waveform 210, subsequent to t,. This current continues toincrease until it reaches a certain threshold level at time t at whichtime the current detector 115 responds to the increasing current.

The current detector 115 at time t applies a signal to the switchcontrol 120. The switch control 120 in response to the activated currentdetector 115 opens the switch 105. An inertial current continues to flowin the inductor 110 due to the stored flux energy therein. The reversevoltage in the inductor 110, due to the decay of the stored fluxtherein, increases the inductor potential at the point A to the positivelevel 212 as shown in FIG. 2. This positive potential activates thecurrent source disabler 135. The activated current source disabler 135applies an inhibit signal to the current source 130. The current outputof the current source 130 in response to the inhibit signal drops to ano current zero level 232 as shown in F 16. 2.

The voltage level 212 at point A, subsequent to time 1 forward biasesdiode 112 and a load current flows through the diode 112 and the lowpass filter 113 to a load connected to output terminal 140. The voltagelevel 222 at the output terminal 140 exceeds the threshold level 225,shown in wavefonn 220, above which level the threshold detector 125 isdeactivated. The low pass filter 113 is included to reduce variations inthe output voltage due to the switching action of the regulator. Thevariation shown in waveform 220 is exaggerated from illustrativepurposes. The actual variation in the regulated voltage is very small.

Current continues to flow in the inductor 110 until the stored flux isdissipated at time 1 When the inductor 110 ceases to conduct current,the voltage level at point A drops to the ground potential 213 as shownin H0. 2. The diode 112 in response to this voltage is back biased andthe load current flowing to filter 113 is tenninated. Accordingly thevoltage at the output terminal 140 begins to decay toward the thresholdlevel 225 at point 223.

The existing ground potential at point A, shown as voltage 213 in FIG.2, deactivates the current source disabler 135 permitting the currentsource 130 to turn on at time t, to its low current level state shown bycurrent level 233 in FIG. 2. initially the total current drawn by thecurrent source 130, just subsequent to time is drawn through theresistor 117. However as the'output voltage decreases toward voltagelevel 225 at time I, the current flow through resistor 117 decreases invalue below the current level drawn by the current source 130. Thedifference in current is hence drawn from the threshold detector 125.The difference current is sutficient to initiate the tum-on of thethreshold detector 125. The threshold detector 125 in turning on turnson the switch control 120 which applies a current level control signal,via lead 126, to the current source 130. This current level controlsignal switches the current source 130 into its higher current levelstate at the time 1 This high level current state is shown by thecurrent level 234 in FIG. 2. With the current source 130 in its highlevel current state the threshold detector 125 in its high level currentstate the threshold detector 125 is rapidly switched into its fullmaximum operating state. The rapidly switched threshold detector 125, inturn, rapidly switches the switch control 120 into its full maximumoperating state. The switch control 120 in its full maximum operatingstate rapidly closes the switch 105. The switch remains closed until thecurrent detector is activated whereupon the abovedescribed cycle ofoperation is repeated.

It is apparent from the foregoing that by utilizing the two levelcurrent source 130 to accelerate the switching action of the thresholddetector 125, the switching action of the switch 105 rapidlyaccelerated. Hence the switching transition period during which power isdissipated in the switch 105 is significantly reduced.

The two level current source 130 additionally functions to regulate themagnitude of the output voltage at the output terminal 140 which isgreater than any other voltage in the circuit including the sourcevoltage. When the inductor voltage at point A exceeds a certain level,the current source 130 is disabled by the current source disabler 135.When the current in the resistor 117 decreases below a certain thresholddue to a decline in the output voltage, the threshold detector is activated and in turn activates the current source 130. This thresholdcurrent is the low level current capacity of the current source 130,shown as current level 233 in FIG. 2. The activated current source drawsa larger current through the resistor 117 until the inductor voltageagain brings about its disablement. This arrangement readily permitsregulation of the output voltage without resort to conventional voltagecomparison techniques.

A detailed circuit schematic of the switching regulator is shown in FIG.3. 1n the circuit shown in H0. 3, two compound connected switchingtransistors 305 and 306 are utilized'as the switching device which isdesignated in FIG. 1 as switch 105. The transistor 325 performs thefunctions of the threshold detector 125 and the switch control 120. Thecurrent source 339 performs the function of the current source 130 andthe transistor 335 performs the function of the current source disabler135.

The closing of the manual switch 302 at the time t, couples the negativevoltage source 301, via the transistors 305 and 306, to the energystorage inductor 310. With the transistors 305 and 306 biased into aconducting state, current flows from ground, via the inductor 310, tothe negative voltage source 301. The capacitor 380 and resistor 381shunting the inductor 310 are included to suppress ringing transientswhich may be generated as the inductor 310 is repeated connected to anddisconnected from the source 301. A current detecting resistor 309 isincluded in this current condition path and is utilized to generate athreshold control signal to control the current detector circuitry 390which in turn activates the holding circuit 319 comprising transistors321 and 322.

The transistor 330, which is included in the current source circuitry339, is at this time subsequent to t, in the conducting state designatedby current level 231 in FIG. 2. This current flows through the resistor317 and through the collectoremitter path of transistor 330. Thetransistor 330 is drawing a current determined by the bias voltageestablished by Zener diode 331, which is in excess of the currenttraversing the resistor 317. This excess current is drawn from thetransistor 325 and biases it into a saturated condition. With transistor325 saturated, the switching transistors 305 and 306 in their activeregion just prior to t are rapidly biased into saturation. Hence, asdescribed above, a current begins to flow from ground through inductor310 to the negative voltage source 301.

As the current flowing through the inductor 310 increases in magnitude,the voltage drop generated across the current detector-resistor 309increases. The voltage drop across the resistor 309 is applied to thecapacitor 308 and thence to the emitter electrode of the transistor 321.When the voltage of capacitor 308 exceeds a predetermined thresholdvalue as set by Zener diode 307 at time t the transistors 321 and 322are biased into their conducting state. The transistor 321 is connectedto the transistor 322 in a compound connection to form a holding circuit319. This holding circuit is functionally a part of the current detector115 as shown in FIG. I and serves merely to cause the switch control 120to release the switch 105. The operation of such holding circuits iswell known in the art and hence is not discussed herein in detail.

' With the transistors 321'and 322 conducting current, the currentoutput of the transistor 325 is diverted from the base electrode of thetransistor 306. Hence the transistors 305 and 306 are biased into anonconducting state. As is apparent to those skilled in the art, thetransistors 321 and 322 remain in their conducting state until thecharge stored on capacitor 308 is fully discharged.

The switching transistors 305 and 306 are biased into a nonv conductingstate by the diversion of the current output of transistor 325 to theholding circuit 319 and accordingly no energy is supplied to theinductor from source 301. The stored flux in the inductor 310 begins todecay and the resultant induced reverse voltage therein forwardbiasesthe diodes 312 and 313. The inertial current of the inductor 110 istransmitted, via the diode 313, to the base electrode of the transistor335 biasing it into a nonconducting state. With the transistor 335 in anonconducting state the transmission of current through the Zener diode331 of the current source 339 is disabled. The current source transistor330 is accordingly biased into a nonconducting state thereby disablingthe generation of current by the current source 339.

The inertial current supplied by the inductor 310 flows through the nowforward biaseddiode 312, the low pass filter 314 and a load circuitconnected to output terminal 340. A

small portion of the load current is diverted through the resistor 317and the varistor 318 to ground. A positive voltage approximating thewaveform 220 in FIG. 2 is supplied at the output terminal 340. Due tothe eventual dissipation of the stored flux in the inductor 310, theoutput voltage begins to decline in value subsequent to time t,,. Atthis time 1 the voltage at the inductor 310 has declined sufficientlydue to the dissipation of its stored flux to permit the transitor 335 toconduct current.

With transistor 335 conducting, a current path is completed from groundto negative source 301 permitting a current flow in the Zener diode 331.Accordingly the current source 339 begins to conduct current as thetransistor 330is biased into a conducting state. The transistor 330conducts a current indicated by the current level 233 in FIG. 2. Thiscurrent level is determined by the resistance magnitude of the resistors332 and 333 which are connected to the collector-emitter path of thetransistor 330. The current drawn by current source 339 is a constantdefined by level 233. To maintain this level, as the current in resistor317 decreases, current must be drawn from the base electrode oftransistor 325. In response to this current drain the transistor 325. isbiased into its active conducting state.

With the transistor 325 biased into its active conducting state, acurrent is transmitted, via resistors 323 and 324, to the base electrodeof transistor 306 and from thence to source 301. In response to thiscurrent the transistors 305 and 306 start to switch into their activeconducting state.

The current traversing the collector-emitter path of transistor 325 tothe source 301 slowly increases in magnitude. At time the voltage dropacross resistors 323 and 324 becomes sufficient to bias the transistor327 into a conducting state. With transistor 327 conducting the resistor332 in short circuited and hence removed from the emitter circuit of thecurrent source transistor 330. Hence the current traversing thecollector-emitter path of the current source transistor 330 isimmediately increased to the higher current level 234, shown in FIG. 2,which in the illustrative embodiment is double its lower level value.

The increased higher level current'traversing the collectoremitter pathof the transistor 330 rapidly drives the transistor 325 into itssaturation conducting state. The transistor 325 in its fully saturatedconducting state, in turn, rapidly drives the transistors 3.05 and 306into their fully saturated conducting state. The rapid turn-on of thetransistors 305 and 306 significircuit 319 into conduction and henceturn off the transistors I 305 and 306 to repeat the regulation cycle.

It is apparent from the foregoing that the current source 339 in itsresponse to the voltage of inductor 310 regulates the magnitude of theoutput voltage at output terminal 340 in addition to increasing theswitching speed of transistors 305 and 306.

I claim:

1. A switching type regulator comprising, a switching device, aswitching control to open and close said switching device, a-source ofenergy, an energy storage element, said switching device connecting saidsource of energy to said energy storage element, an output controlimpedance coupled to said energy storage element, said switching controlincluding means responsive to a particular threshold of the energytransmitted to said output control impedance from said energy storageelement, said switch control being activated at said particularthreshold and closing said switching device, a current generator coupledto said load output control impedance having at least two alternatecurrent paths representing a lower and upper current levelstate controland means to switch said current generator into the upper of its twocurrent level states by switching said current paths when-said switchcontrol initially responds to the energy transmitted to said outputcontrol impedance whereby the increased current generated by saidcurrent generator accelerates the closing of said switch by acceleratingthe said response of said switch control.

2. A switching type regulator as defined in claim 1 wherein one of saidcurrent paths of said two level current source includes a limitingimpedance to limit the current generated therein and said-means toswitch comprises another one of said current paths including asemiconductor switch shunting said impedance to bypass said impedanceand increase the current generated therein.-

3. A switching type regulator as defined in claim 2 further includingmeans to disable the operation of said current source subsequent to theclosing of said switching device.

4. A switching type regulator as defined in claim 3 further includingcurrent detector means to respond to a predetermined threshold ofcurrent flowing through said energy storage element and means totransmit signals coupled to said switch control and responsive to saidcurrent detector means to divert activating signals generated by saidcurrent source from said switching control whereby said switchingcontrol is deactivated.

5. A switching apparatus in which a first electrical signal isrepeatedly connected to and disconnected from an energy storage elementin order to supply a second electrical signal at an output circuit,comprising a semiconductor switch including 'a control electrode andhaving its transconductive path connecting said first electrical signalto said energy storage element, means connected to said controlelectrode to energize said semiconductor switch into a conductingcondition including a driver transistor having its base electrodecoupled to said output circuit, a multilevel current source having lowand high current outputs controlled by a variable current pathimpedance, said current source coupled to said base electrode and saidoutput circuit whereby a drop in current in said output circuit allowsthe transfer of sufficient current to bias said driver transistor into aconductive state and means to increase the level of operation of saidcurrent source from its low to its high current output by reducing saidcurrent path impedance in response to initial current flow in saiddriver transistor whereby said driver transistor is more rapidlyswitched into its conductive state.

means to increase the level of operation comprises means to bypass aselected number of said plurality of impedances.

1. A switching type regulator comprising, a switching device, aswitching control to open and close said switching device, a source ofenergy, an energy storage element, said switching device connecting saidsource of energy to said energy storage element, an output controlimpedance coupled to said energy storage element, said switching controlincluding means responsive to a particular threshold of the energytransmitted to said output control impedance from said energy storageelement, said switch control being activated at said particularthreshold and closing said switching device, a current generator coupledto said load output control impedance having at least two alternatecurrent paths representing a lower and upper current level state controland means to switch said current generator into the upper of its twocurrent level states by switching said current paths when said switchcontrol initially responds to the energy transmitted to said outputcontrol impedance whereby the increased current generated by saidcurrent generator accelerates the closing of saId switch by acceleratingthe said response of said switch control.
 2. A switching type regulatoras defined in claim 1 wherein one of said current paths of said twolevel current source includes a limiting impedance to limit the currentgenerated therein and said means to switch comprises another one of saidcurrent paths including a semiconductor switch shunting said impedanceto bypass said impedance and increase the current generated therein. 3.A switching type regulator as defined in claim 2 further including meansto disable the operation of said current source subsequent to theclosing of said switching device.
 4. A switching type regulator asdefined in claim 3 further including current detector means to respondto a predetermined threshold of current flowing through said energystorage element and means to transmit signals coupled to said switchcontrol and responsive to said current detector means to divertactivating signals generated by said current source from said switchingcontrol whereby said switching control is deactivated.
 5. A switchingapparatus in which a first electrical signal is repeatedly connected toand disconnected from an energy storage element in order to supply asecond electrical signal at an output circuit, comprising asemiconductor switch including a control electrode and having itstransconductive path connecting said first electrical signal to saidenergy storage element, means connected to said control electrode toenergize said semiconductor switch into a conducting condition includinga driver transistor having its base electrode coupled to said outputcircuit, a multilevel current source having low and high current outputscontrolled by a variable current path impedance, said current sourcecoupled to said base electrode and said output circuit whereby a drop incurrent in said output circuit allows the transfer of sufficient currentto bias said driver transistor into a conductive state and means toincrease the level of operation of said current source from its low toits high current output by reducing said current path impedance inresponse to initial current flow in said driver transistor whereby saiddriver transistor is more rapidly switched into its conductive state. 6.A switching apparatus as defined in claim 5 whereby said variablecurrent path impedance includes a plurality of impedances connected tosaid multilevel current source and said means to increase the level ofoperation comprises means to bypass a selected number of said pluralityof impedances.